1. Field of the Invention
The invention relates to the field of integrated circuits, in particular to integrated circuit packaging.
2. Description of Related Art
Programmable logic device (PLD) integrated circuits have facilitated the miniaturization of electronic devices by permitting a design engineer to replace a large number of specific-function logic ICs with a single IC without the high cost of fabricating a custom integrated circuit. Programmable logic devices are often structured internally as a large array of identical functional logic elements. The exact functioning of each logical element and the interconnections between them is programmed into the PLD before operation. The internal architectures of PLD's can vary but frequently a number of PLD's will share the same internal architecture and operating characteristics and be marketed as a family. The distinction between members in the family is the total number of functional logic elements included in each member.
It is not uncommon for a design engineer working with a PLD to use a member of a device family having a large number of functional logic elements. This guarantees that an adequate number of logic elements will be available and usually permits the engineer to generate and process additional signals at design time that are useful for testing and troubleshooting. When the design is completed a smaller member of the PLD family is selected for production use to reduce costs. Up until now, however, this meant redesigning the circuit board that holds the PLD device. Despite their common internal architecture that allowed migration between different packages in the family, their external packaging did not readily support migration. Consequently, there is a need in the art for integrated circuit packaging that ensures a migration path between related integrated circuits.